1. Field of the Invention
The present invention relates to a method of fabricating a poly-silicon layer and, more particularly, to a method using a Rapid Thermal Annealing (RTA) process.
2. Description of Related Art
Poly-Si (poly-silicon) has superior electrical properties over amorphous silicon (a-Si) as well as the advantage of lower cost than the single silicon crystal. Therefore, it has received a lot of attention in the field of TFT productions recently. Also, poly-Si has played an important role in the application of TFT liquid crystal displays (LCD).
However, the grain size of poly-Si has a great limitations on the electron mobility and device properties. In particular, the grain boundaries existing in poly-Si will be an obstacle for the charge carriers in the device when passing through the gate channel. Therefore, how to enlarge the grain size of poly-Si and thus reduce the number of grain boundaries for enhancing the TFT device properties is an important trend in the poly-Si thin film fabrication technology nowadays. Take the display technology as an example, it is an urgent need to produce highly-efficient TFT's in order to develop better flat-panel displays.
As in U.S. Pat. No. 6,642,092, to Voutsas et al., a method is disclosed of providing a poly-Si component on a metal substrate by using a solid phase crystallization (SPC) annealing process. However, the method is not suitable to be used in providing flat panel displays because the metallic substrate cannot allow light transmission (e.g. backlight transmittance). Also, in the patent of WO2007064087, UM PYUNG-YONG et al. proposes a method using chemical vapor deposition (CVD) to produce poly-Si. The granules sizes of the poly-Si obtained from the both above methods are very small, the diameter is merely about 100 nm, thus the characteristic of the poly-Si layers formed by the above methods is not good enough for flat panel display manufacture.
Currently, the most commonly used method in fabricating the poly-Si thin film is the excimer laser annealing technology. Although a grain size of about 600 nm can be achieved in this case, it is still insufficient for making high-performance flat-panel displays. Therefore, a metal-induced lateral crystallinity (MILC) method was disclosed in TW256,733. The method uses metal, such as nickel, as an inducing material under high temperature and over a long period of time to grow poly-Si. Hence, it is time consuming and the problem of metal pollution will further exist.
Therefore, a solution of solving the above problems of preparing poly-Si, i.e. excessively time consuming, high temperature processing, limitation of the substrate material, pollution from the metal substrate, is an urgent important need. Also, the method of growing a poly-Si with large granule size, high crystallinity, low pollutant, and excellent electrical characteristic will be the main target for the present researchers.